Glass is typically made of silicates that are melted to form a clear, transparent, solid material. The fundamental molecular structural unit of conventional glass is a SiO44− tetrahedron. Ordinary float glass (named for its production process whereby a molten ribbon of glass is floated on molten metal to provide a smooth surface) includes additional amounts of soda (Na2O), usually in the form of sodium carbonate or nitrate during the production process, lime (CaO) and other oxides (usually aluminum and magnesium oxides) to form a soda-lime-silica structure known colloquially as soda-lime glass. Other specialized glass can be prepared by the introduction of other additives and constituents.
It is sometimes highly desirable for conventional glass to have hydrophobic (water repellant) surface properties when employed in certain end-use applications, such as for automotive window glass and other articles that may be subjected to humid environments (e.g., shower stall doors, ceramic tiles and the like). Various proposals exist to impart hydrophobic (water-repellant) properties to glass substrates. For example, U.S. Pat. Nos. 4,263,350, 4,274,856, 5,665,424 and 5,723,172 (the entire content of each being incorporated expressly hereinto by reference) disclose generally that glass surfaces can be coated with a vapor deposited layer of an chloroalkylsilane, such as dimethyidichlorosilane (DMDCS) so as to improve their hydrophobicity and/or release properties. Other proposals exist whereby a fluoroalkylsilane (FAS) coating may be employed to “cap” an underlayer on a glass substrate so as to improve coating durability. Please see in this regard, U.S. Pat. Nos. 5,328,768, 5,372,851, 5,380,585 and 5,580,605 (the entire content of each being incorporated expressly hereinto by reference). In addition, International Application WO 00/25938 (the entire content of which is expressly incorporated hereinto by reference) discloses that a silicon film consisting of chains of siloxane groups each terminating in an end molecule which reacts with water to form an OH group, may be capped by further reaction of that OH group with trimethylchlorosilane to form trimethylchlorosiloxane.
U.S. Pat. No. 6,743,516 to Murphy et al (the entire content of which is expressly incorporated hereinto by reference) discloses coated substrates (preferably glass) which exhibit improved hydrophobicity and durability, as well as methods of imparting such improved hydrophobicity and durability to the substrates. In some of the especially preferred embodiments disclosed therein, coated substrates and methods are provided which include a SiOx-containing anchor layer comprised of a controllably humidified vapor phase deposition of a chlorosilyl group containing compound (typically silicone tetrachloride), and a hydrophobic capping layer chemically bonded to the SiOx-containing anchor layer.
Published International application WO 2004/009505 (the entire content of which is expressly incorporated hereinto by reference) discloses that hydrophobic coatings may be formed on a transparent substrate by treating the surface of the substrate with a mixture or reaction product of a silicone fluid and a solvent. Most preferably the silicone fluid is an alkyl silane or a polysiloxane having a functional group capable of a condensation reaction with hydroxyl. Preferred solvents are those which are miscible with the silicone fluid, such as alcohols, ethers, esters or C1 to C40 hydrocarbons.
In commonly owned U.S. patent application Ser. No. 10/771,514 filed on Feb. 5, 2004 now U.S. Pat. No. 7,138,186 (the entire content of which is expressly incorporated hereinto by reference), it is disclosed that certain performance enhancements can be imparted to hydrophobic coatings, such as enhanced chemical and weather resistance, by the vapor deposition of methyltrichlorosilane over a SiOx-containing anchor layer on transparent substrates (e.g., glass) so as to form a film of polymethylsilsesquioxane thereon. Specifically, in accordance with such application, substrates are provided which have a hydrophobic surface coating comprised of the reaction products of methyltrichlorsilane (MTCS) and dimethyidichlorosilane (DMDCS).
Octadecyltrichlorosilane (OTS) is also known to form a self assembled monolayer (SAM) on oxide surfaced from such materials as silicon. Specifically, U.S. Pat. No. 5,071,709 to Berquier et al (the entire content of which is expressly incorporated herein by reference) discloses the use of OTS dissolved into a mixture of aliphatic hydrocarbon and chlorinated solvents, for example dichloromethane, trichloromethane and the like, for providing an anti-icing coating on automotive windshields. The OTS coating provides for a high degree of hydrophobicity therefore preventing water sheeting and thus ice formation since discreet ice crystals are known to be much easier to remove than a continuous ice sheet. Those skilled in the art will recognize, however, that toluene and other solvents such as benzene are hazardous volatile compounds that require care to avoid environmental issues. In addition, chlorinated solvents are particularly hazardous from a human health perspective and the workspace must be carefully controlled to avoid excessive human exposure. Also, it will be appreciated that that when suing a solvent such as toluene, the solution may de-wet from the surface as the coating is forming which could lead to a lower density coating than was intended or may be required.
Therefore, while the coatings described above certainly provide hydrophobic properties, there is a continual need to improve and/or enhance the same. For example, it would be especially desirable if a more environmentally friendly solvent could be employed for OTS which wets well on glass surfaces and does not de-wet as the coating develops. It is towards providing such improvements and/or enhancements that the present invention is directed.
Broadly, the present invention is embodied in liquid coating solutions which impart hydrophobicity to substrate surfaces (e.g., glass) and include a silane dissolved in a liquid paraffinic solvent. Most preferably the silane is octadecyltrichlorosilane (OTS). Preferred liquid paraffinic solvents are normal (straight chain) liquid parrafins having between 10 to 20 carbon atoms per molecule exhibiting flash points (ASTM D93) of between about 70° C. to about 160° C., and initial boiling points (ASTM D86) of between about 185° C. to about 300° C. The OTS will be present in the hydrophobic solutions in amounts sufficient to form a hydrophobic coating on surfaces of substrates on which the solutions are applied, and most preferably will be present in amounts ranging between about 0.25 to about 2.5 molar. Applying a coating of the solution onto a substrate surface will allow the OTS for form a self-assembled monolayer thereon imparting hydrophobicity to the substrate as determined by a high contact angle of at least about 100°.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.